Poly(vinyl butyral) (PVB) is commonly used in the manufacture of polymer sheets that can be used as interlayers in light-transmitting laminates such as safety glass or polymeric laminates. Safety glass typically refers to a transparent laminate comprising a poly(vinyl butyral) sheet disposed between two panes of glass. Safety glass often is used to provide a transparent barrier in architectural and automotive openings. Its main function is to absorb energy, such as that caused by a blow from an object, without allowing penetration through the opening.
Safety glass can be formed by a process in which two layers of glass and a plastic interlayer, such as poly(vinyl butyral), are assembled into a pre-press, tacked into a pre-laminate, and finished into an optically clear laminate. The assembly phase can involve laying down a piece of glass, overlaying a poly(vinyl butyral) sheet on that glass, laying down a second piece of glass on the poly(vinyl butyral) sheet, and then trimming the excess poly(vinyl butyral) to the edges of the glass layers.
The plastic interlayer can be produced by mixing poly(vinyl butyral) polymer with one or more plasticizers, and optionally with one or more other ingredients, and melt processing the mix into sheeting, which can be collected and rolled for storage and transportation.
In addition to various common uses for laminated glass structures having a conventional polymer sheet type interlayer, in some applications of laminated safety glass it is particularly desirable to have additional fire retardation features. Examples of attempts to include some measure of fire retardation include the inclusion of additional layers of intumescent material that are specifically designed to char when subjected to flames, thereby preventing the further spread of a fire through the charred layer (U.S. Pat. No. 4,485,601). Additional protection, however, is often desirable.
Accordingly, there is a need in the art for multiple layer glass panels and interlayers used therein that provide the desired fire resistance while also allowing for the facile manufacture of a polymer sheet without adversely affecting other desirable properties.